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          <th colspan="3" align="center">Added PRAGMAs</th>
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          <td width="20%" align="left"><a accesskey="p" href="changedpragmas.html">Prev</a> </td>
          <th width="60%" align="center">Chapter 1. Berkeley DB SQL: The Absolute Basics</th>
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    <div class="sect1" lang="en" xml:lang="en">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both"><a id="addedpragmas"></a>Added PRAGMAs</h2>
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        </div>
      </div>
      <div class="toc">
        <dl>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#bdbsql_error_file">PRAGMA bdbsql_error_file</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#bdbsql_lock_tablesize">PRAGMA bdbsql_lock_tablesize</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#bdbsql_shared_resources">PRAGMA bdbsql_shared_resources</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#bdbsql_single_process">PRAGMA bdbsql_single_process</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#bdbsql_system_memory">PRAGMA bdbsql_system_memory</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#bdbsql_vacuum_fillpercent">PRAGMA bdbsql_vacuum_fillpercent</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#bdbsql_vacuum_pages">PRAGMA bdbsql_vacuum_pages</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#multiversion">PRAGMA multiversion</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#snapshot_isolation">PRAGMA snapshot_isolation</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#trickle">PRAGMA trickle</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#txn_bulk">PRAGMA txn_bulk</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="addedpragmas.html#replication_pragmas">Replication PRAGMAs</a>
            </span>
          </dt>
        </dl>
      </div>
      <p>
                The following PRAGMAs are added in the Berkeley DB SQL interface.
            </p>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="bdbsql_error_file"></a>PRAGMA bdbsql_error_file</h3>
            </div>
          </div>
        </div>
        <pre class="programlisting">PRAGMA bdbsql_error_file [filename]</pre>
        <p>
                    Redirects internal Berkeley DB error messages to
                    the named file. If a relative path is specified to
                    <code class="literal">[filename]</code>, then the path is
                    interpreted as being relative to the current
                    working directory.
                </p>
        <p>
                    If this PRAGMA is issued with no filename, then the
                    current target for Berkeley DB error output is
                    returned. By default, error messages are sent to
                    <code class="literal">STDERR</code>.
                </p>
        <p>
                    This PRAGMA can be issued at any time; initial
                    database access does not have to occur before this
                    PRAGMA can be used.
                </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="bdbsql_lock_tablesize"></a>PRAGMA bdbsql_lock_tablesize</h3>
            </div>
          </div>
        </div>
        <pre class="programlisting">PRAGMA bdbsql_lock_tablesize [= N]</pre>
        <p>
                    Sets or reports the number of buckets in the Berkeley DB environment's 
                    lock object hash table.
                </p>
        <p>
                    This pragma must be called prior to opening/creating the
                    database environment.
                </p>
        <p>
                    For more details, see
                    <a href="../api_reference/C/envget_lk_tablesize.html" class="olink">get_lk_tablesize</a>
                    and 
                    <a href="../api_reference/C/envset_lk_tablesize.html" class="olink">set_lk_tablesize</a>.
                </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="bdbsql_shared_resources"></a>PRAGMA bdbsql_shared_resources</h3>
            </div>
          </div>
        </div>
        <pre class="programlisting">PRAGMA bdbsql_shared_resources [= N]</pre>
        <p>
                    Sets or reports the maximum amount of memory (bytes) to be
                    used by shared structures in the main environment region.
                </p>
        <p>
                    This pragma must be called prior to opening/creating the
                    database environment.
                </p>
        <p>
                    For more details, see
                    <a href="../api_reference/C/envget_memory_max.html" class="olink">get_memory_max</a>
                    and 
                    <a href="../api_reference/C/envset_memory_max.html" class="olink">set_memory_max</a>.
                </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="bdbsql_single_process"></a>PRAGMA bdbsql_single_process</h3>
            </div>
          </div>
        </div>
        <pre class="programlisting">PRAGMA bdbsql_single_process = boolean</pre>
        <p>
                    To create a private environment rather than a shared
                    environment, enable this pragma. The cache and other
                    region files will be created in memory rather than
                    using file backed shared memory.
                </p>
        <p>
                    In Berkeley DB SQL the default behavior is to allow a
                    database to be opened and operated on by multiple
                    processes simultaneously. When this pragma is enabled,
                    accessing the same database from multiple processes
                    simultaneously can lead to data corruption. Either
                    option supports accessing a database using a single
                    process multi-threaded application.
                </p>
        <p>
                    By default omit sharing is disabled. This pragma must
                    be called prior to opening/creating the database
                    environment.  Because the setting is not persistent,
                    you may need to invoke it before every database open,
                    or define compile option
                    <code class="literal">BDBSQL_OMIT_SHARING</code> instead.
                </p>
        <p>
                    For more information, see <a href="../programmer_reference/env_region.html" class="olink">Shared memory region</a>. Note that this
                    pragma causes the <a href="../api_reference/C/envopen.html#envopen_DB_PRIVATE" class="olink">DB_PRIVATE</a> flag to be specified in 
                    the <a href="../api_reference/C/envopen.html" class="olink">DB_ENV-&gt;open()</a> method.
                </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="bdbsql_system_memory"></a>PRAGMA bdbsql_system_memory</h3>
            </div>
          </div>
        </div>
        <pre class="programlisting">PRAGMA bdbsql_system_memory [base segment ID]</pre>
        <p>
                    Queries or sets a flag that causes the database's
                    shared resources to be created in system shared
                    memory. By default the database's shared resources
                    are created in file-backed shared memory. 
                </p>
        <p>
                    If a [base segment ID] is specified, the shared
                    resources will be created using X/Open style shared
                    memory interfaces. The [base segment ID] will be
                    used as the starting ID for shared resources used
                    by the database. Use different [base segment ID]
                    values for different databases. It is possible for
                    multi-process applications to use a single database
                    by specifying the same [base segment ID] to this
                    PRAGMA. Each connection needs to set this PRAGMA.
                </p>
        <p>
                    This PRAGMA may be used to set a [base segment ID]
                    only before the first table is created in the
                    database.
                </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="bdbsql_vacuum_fillpercent"></a>PRAGMA bdbsql_vacuum_fillpercent</h3>
            </div>
          </div>
        </div>
        <pre class="programlisting">PRAGMA bdbsql_vacuum_fillpercent [= N]</pre>
        <p>
                    Sets or reports the page full threshold. 
                    Any page in the database that is at or below this
                    percentage full is considered for vacuuming when
                    <code class="literal">PRAGMA incremental_vacuum</code> is
                    enabled.  The value is specified as a percentage
                    between 1 and 100.  By default, pages 85% full and
                    below are considered for vacuuming.
                </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="bdbsql_vacuum_pages"></a>PRAGMA bdbsql_vacuum_pages</h3>
            </div>
          </div>
        </div>
        <pre class="programlisting">PRAGMA bdbsql_vacuum_pages [= N]</pre>
        <p>
                    Sets or reports the maximum number of pages to be
                    returned to the file system from the free page list
                    when incremental vacuuming is enabled. By
                    default, up to 128 pages are removed from the free
                    list.
                </p>
        <p>
                    Page vacuuming is controlled using 
                    <a class="xref" href="changedpragmas.html#auto_vacuum" title="PRAGMA auto_vacuum">PRAGMA auto_vacuum</a>.
                </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="multiversion"></a>PRAGMA multiversion</h3>
            </div>
          </div>
        </div>
        <pre class="programlisting">PRAGMA multiversion</pre>
        <p>
                    Controls whether Multiversion Concurrency Control (MVCC) is on
                    or off. You can not use this PRAGMA at any time during
                    your application's runtime after your database tables
                    have been accessed.
                </p>
        <p>
                    For more information on MVCC and snapshot isolation,
                    see <a class="xref" href="mvcc.html" title="Using Multiversion Concurrency Control">Using Multiversion Concurrency Control</a>
                </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="snapshot_isolation"></a>PRAGMA snapshot_isolation</h3>
            </div>
          </div>
        </div>
        <pre class="programlisting">PRAGMA snapshot_isolation</pre>
        <p>
                    Controls whether snapshot isolation is turned on. This
                    PRAGMA can be used at any time during your
                    application's runtime <span class="emphasis"><em>after</em></span>
                    Multiversion Concurrency Control (MVCC) has been turned on.
                </p>
        <p>
                    For more information on MVCC and snapshot isolation,
                    see <a class="xref" href="mvcc.html" title="Using Multiversion Concurrency Control">Using Multiversion Concurrency Control</a>
                </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="trickle"></a>PRAGMA trickle</h3>
            </div>
          </div>
        </div>
        <pre class="programlisting">PRAGMA trickle [percent]</pre>
        <p>
                    Ensures that at least the specified percentage of
                    pages in the shared cache are clean. This can cause
                    pages that have been modified to be flushed to
                    disk.
                </p>
        <p>
                    The trickle functionality enables an application to
                    ensure that a page is available for reading new
                    information into the shared cache without waiting
                    for a write operation to complete.
                </p>
        <p>
                    Specifying this PRAGMA without a percentage value
                    causes the current trickle value to be displayed.
                    Specify <code class="literal">0</code> to turn the trickle
                    functionality off.
                </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="txn_bulk"></a>PRAGMA txn_bulk</h3>
            </div>
          </div>
        </div>
        <pre class="programlisting">PRAGMA TXN_BULK</pre>
        <p>
                    Enables transactional bulk loading optimization.
                    For more information, see
                    <a class="xref" href="dbfeatures.html#bulkloading" title="Using Bulk Loading">Using Bulk Loading</a>.
                </p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="replication_pragmas"></a>Replication PRAGMAs</h3>
            </div>
          </div>
        </div>
        <p>
                    Seven PRAGMAs were added to control replication.
                    They are described in 
                    <a class="xref" href="sqlrep.html" title="Chapter 4. Using Replication with the SQL API">Using Replication with the SQL API</a>:
                </p>
        <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
          <h3 class="title">Note</h3>
          <p>
                        If you are using these replication PRAGMAs and you
                        want to perform a backup, there is an additional
                        backup step for the pragma file. See
                        <a class="xref" href="admin.html#backup" title="Backing Up Berkeley DB SQL Databases">Backing Up Berkeley DB SQL Databases</a>
                        for more information.
                    </p>
        </div>
        <div class="itemizedlist">
          <ul type="disc">
            <li>
              <p>
                            <span class="bold"><strong>PRAGMA replication</strong></span>
                        </p>
            </li>
            <li>
              <p>
                            <span class="bold"><strong>PRAGMA replication_initial_master</strong></span>
                        </p>
            </li>
            <li>
              <p>
                            <span class="bold"><strong>PRAGMA replication_local_site</strong></span>
                        </p>
            </li>
            <li>
              <p>
                            <span class="bold"><strong>PRAGMA replication_remote_site</strong></span>
                        </p>
            </li>
            <li>
              <p>
                            <span class="bold"><strong>PRAGMA replication_remove_site</strong></span>
                        </p>
            </li>
            <li>
              <p>
                            <span class="bold"><strong>PRAGMA replication_verbose_output</strong></span>
                        </p>
            </li>
            <li>
              <p>
                            <span class="bold"><strong>PRAGMA replication_verbose_file</strong></span>
                        </p>
            </li>
          </ul>
        </div>
      </div>
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